Since I'm surprised at the recent reviews I have read for other GTD applications, I thought it would be useful to add a review for Thinking Rock.
Out of all the applications I have tried, Thinking Rock is one of the few that follows David Allen's GTD methodology in detail.
The developer is very responsive, bugs have been fixed and requests have been incorporated into the application. Right now Thinking Rock is quite impressive for a version 1 software, especially given that it is available for free. I would encourage people who find the application useful to donate and show their support.
For comparison, here are some of the applications I have tried:
1. Kinkless GTD. Great and free, but requires OmniOutliner Pro. For me Thinking Rock has been easier to use on a daily basis. Perhaps OmniFocus will eventually be a great GTD program, but for now I prefer Thinking Rock.
2. Midnight Inbox. Looks beautiful, but it lacked a lot of functionality for my use.
3. iGTD. It's very rapidly evolving, but at the moment still lacks some GTD features (e.g., Waiting For, Delegated, Reports, etc.)
4. Actiontastic. Again, looks interesting but lacks functionality (e.g, Delegated, Waiting For, viewing multiple projects at once, etc.)
These 4 programs come to mind since they are recent, but I have used others and always return to Thinking Rock. My advice is to download them, use them, and compare them. Each person has different tastes and preferences. My choice is Thinking Rock since it allows me to follow the GTD methodology, enables me to print a variety of reports (e.g., by context, by person, by project, etc.), allows me not only to view but also to sort multiple items using different criteria (e.g., action, project, context, etc.), has a very useful pop-up help, works on Windows and Mac (this was particularly important since I had to move back and forth between a PC and my Mac for some projects), has a very detailed Help file, and is very easy to use. After a couple of times of using it I was getting things done with the help of the application, and I TRUSTED the application. This is essential for GTD, and I can't say the same thing about alternative programs.